Process of concentrating carotene and tocopherol in palm oil by thermal difusion



United States Patent C PROCESS 6F CONCENTRATHIG CAROTENE AND ggzHEROL 1NPALE i OIL BY THERMAL DIF- Arthur Letcher dones, Lyndhurst, and ErnestC. Milherger, Maple Heights, Ohio, assignors to The Standard OilCompany, Cleveland, Ghio, a corporation of Ghio No Drawing. ApplicationOctober 31, 1952, Serial No. 318,086

4 Claims. (Cl. 269-666) The present invention relates to a method ofconcentrating, by liquid thermal difiusion, carotene in palm oil andparticularly in resolving palm oil into two fractions, one of which isenriched in carotene, contains a lower percentage of fatty acids thancontained in the initial palm oil and has increased stability againstoxidation, and the other of which is lighter in color.

Among the various vegetable oils that are available, palm oil is uniquein containing an amount of carotene that is relatively large as comparedwith the carotene content of other vegetable oils. The concentration ofcarotene in palm oil usually varies between about 0.05 and 0.20% and itis this relatively large amount of carotene that is believed to beresponsible for the deep orange-red coloring of crude palm oil.

Carotene, which term is intended herein to include alpha-, beta, andgamma carotene, is a provitamin. A, being converted into vitamin A by asplitting of the carotene molecule.

Palm oil contains traces of tocopherols, also known as vitamin E. it isbelieved that the tocopherols in palm oil act as antioxidants and assuch inhibit to a certain extent the oxidation of the carotene and otheringredients. Depending upon the geographical origin of the palm fruitsfrom which it is extracted and the procedure used in extraction, palmoil contains as little as 3% and as much as 45% free fatty acids. Thepresence of free fatty acids in palm oil is objectionable because oftheir relative instability to heat and oxidation.

At present the extraction of carotene from palm. oil is carried out bysaponifying the crude palm oil withsodium hydroxide or potassiumhydroxide and then extracting the resulting soap with ethylenedichloride. While approximately 95% carotene recovery is obtained bythis method, the extremely large amounts of bulk palm oil that must beprocessed to obtain a small amount of carotene, e. g., approximately athousand pounds of palm oil must be handled and separated from thesolvent by centrifuges to obtain a pound of carotene, makes the presentmethod an extremely expensive one and results in a correspondingly highprice for concentrated carotene. In addition the oil is useless for foodand other purposes for which the oil is desirable. It is recoverableonly as the soap which greatly limits the use of the bulk of the oil.

It has now been found that a preliminary concentration of the carotenein palm oil can be obtained by subjecting the crude palm oil to liquidthermal diffusion and that, surprisingly, in effecting suchconcentration the desirable tocopherols are retained with thecarotene-enriched fraction and the concentration of the undesirable freefatty acids is considerably reduced.

It will be apparent that the method of this invention has a number ofimportant advantages, among which are a considerable reduction in thebulk of oil that must he handle to extract carotene by the conventionalsolvent extraction method, a corresponding increase in the capacity ofexisting solvent extraction equipment, and in an increased stabilityagainst oxidation of the oil subjected 2,741,643 Patented Apr. 10, 19.56

lighter colored oils is reflected in the market by the higher prices ofthe light colored oils as compared with those at which the darker oilsare quoted.

Inasmuch as the present invention is concerned primarily with theconcentration of carotene, it is of advantage to utilize the lowergrades of darker colored palm oils as source material for carotene. Animportant ancillary advantage of the method of the invention is that thecarotene-impoverished fraction obtainable by this method is lighter incolor than the initial oil and possesses all of the qualifications ofthe lighter crude palm oils that command higher prices in the market.Thus, the method of the invention is useful not only in theconcentration of the carotene contentin palm oil, but also but. also inconverting the palm oil into a lighter colored. oil, for which there isgreater demand in. the market than the initial and. comparatively darkpalm oil.

It is also to be understood thatthe carotene enriched productobtainableby the method of this invention is suitable for use in purposes otherthan the conventional solvent extraction methods utilized in obtaininghighly concentrated carotene. Thus, for example, the carotene enrichedfractionv is particularly useful as a natural vegetable coloring foraddition to butter, margarine and the like, while. at the same timeincreasing the vitamin A content of such products.

Liquid thermal diffusion, as is kell-known in the art, consistsessentially in forming a thin film of liquid confined by closely-spaced,mutually parallel and opposed surfaces. of heat-conductive materialthat. is inert to the liquid and its components, heating one of thesurfaces to maintain a temperature gradient across the film andaccumulating and Withdrawing from the film two dissimilar fractions, onefraction being concentrated by thermal diffusion adjacent the cooler ofthe two surfaces and the other fraction being concentrated by thermaldiffusion adjacent the hotter of the two surfaces.

Inasmuch as ithas been found that a fraction enriched in carotene andimpoverished infree fatty acids becomes concentrated adjacent the coolersurfaces. by thermal diffusion, the method of this invention in essencecomprises the steps of forming a thin film of palm oil confined. byclosely-spaced, mutually parallel and opposed surfaces ofheat-conductive, inert material, such as glass, stainless steel,aluminum or the like, maintaining a temperature gradient across the filmso formed, and accumulating and withdrawing from the film acarotene-enriched fraction concentrated by thermal diffusion adjacentthe cooler surface.

The thermal diffusion of palm oil may be carried out in a number ofWays. One such way is to fill a vertical slit formed by closely-spaced,mutually parallel and opposed surfaces with the crude palm oil,maintaining a temperature gradient across the slit until the liquid hasseparated into an upper light colored fraction and a lower darkerfraction and then removing the lower fraction which is enriched incarotene and impoverished in fatty acids.

Another method is substantially similar except that the crude palm oilis more or less continuously introduced into the slit at any pointtherein and light and dark colored fractions are more or lesscontinuously removed from the top and the bottom, respectively, of theslit.

A third method is to introduce the crude liquid palm oil continuously orintermittently at one point or area in a thermal difiusion slit, the hotsurface being above the cold surface if the slit is other than vertical,and continuously or intermittently removing, at points or areas remotefrom the point or area of introduction, light and dark colored fractionsfrom adjacent the hot and cold surfaces, respectively, or alternatively,removing the dark fraction at one end of the slit from adjacent the coldjacent the hot surfaceat the other end of the slit.

These modifications all have in common the step of V the hot and coldsurfaces and the further step of ,ac-

cumulating and then withdrawing the fractions so concentrated. Foroptimum results, it is desirable either or both to add an inert andeasily separable material, such as chlorobenzene, for reducing theviscosity of the liquid in the slit and to dehydrate the palm oil beforesubjecting it to thermal difiusion.

The temperature of the hot and cold walls may vary widely so long asthat of the hot wall is not so high as to equal the temperature at whichcarotene decomposes under the conditions of thermal diffusion, bearingin mind the residence time of the palm oil and its components andpresence of a residual anti-oxidant such as tocopherol, or of an addedanti-oxidant, and the temperature of the cold wall is not so low as toequal the congealing temperature of the oil or cause an appreciableincrease in its viscosity. Hot wall temperatures as high as about 300 F.and cold wall temperatures as low as about 105 F. are preferred. Higherhot wall temperatures may be employed .if anti-oxidant is present inamounts sufficient to avoid oxidation of the carotene at such highertemperatures, especially if the residence time of the carotene in theapparatus is relatively short. The extent of separation within thepermissible range is a 7 function of the temperature gradient.

The film must be thin enough to permit the thermal diffusive forces toefiect the separation, and the temperature gradient and withdrawal ratesmust be related to the film dimensions to permit the desired degree ofseparation. Film'thicknesses of the order of about 0.01 to 0.15 inch,preferably between about 0.01 and 0.06 inch, are desirable from thestandpoint of being thin enough to make etfective use of the thermaldifiusive forces and thick enough to make possible the accumulation ofthe separated fractions in different portions of the slit..

It is advantageous, in order to obtain a carotene-enriched fraction ofmaximum concentration, to reduce the rate of withdrawal of said fractionto a small percentage of the rate of withdrawal of thecarotene-impoverished.

fraction. 'This may be accomplished in apparatus wherein the crude palmoil is introduced at a point or area between the ends of the column andthe two fractions are withdrawn at opposite ends and is particularlyeffective in countercurrent and concurrent end feed methods, i. e.,

where the palm oil is introduced at one point or area in the column andthe carotene'enriched fraction is withdrawn at a considerably lowerrate, at a remote point or area from adjacent the cold wall. The ratioof withdrawal rates may desirably be as low' as 5 or even lower and ifdesired the larger volume of carotene-impoverished fraction may beresubjected to continuous thermal difiusion in one or more subsequentthermal difiusion columns.

Inasmuch as crude palm oil frequently contains some water, usually lessthan 1%, and the presence of such' water reduces the eficiency of theprocess, it is desirable to dry the palm oil before it is subjected tothermal diffusion. It is necessary, when operating the method of theinvention in a continuous manner, to introduce the crude palm oil intothe thermal difiusion apparatus in a fluid and not too viscouscondition. To this end, it may be necessary to preheat the palm oil to atemperature of the order of about 110 F., the exact temperaturedepending upon the congealing temperature of the particular palm oil.The advantages and utility of the invention will become further apparentfrom the following examples:

Example 1 An annular slit having a volume of approximatelySO cc., a slitwidth of 0.043 inch and a height of 8 feet, formed by two concentricglass tubes, was filled with crude palm oil. One surface of the slit wasmaintained at a temperature of approximately 212 F. by means of steam atatmospheric pressure, continually passed through the inner tube. Theother surface of the slit, formed by the inner surface of the outertube, was maintained at a temperature of 110 F. by the continuouscirculation of top water through a jacket surrounding the outer tube.After three nights and two days, or approximately 60 hours, it wasobserved that the liquid in the upper portion of the slit was coloredlight orange and that the liquid in the lower portion of the slit was adark red orange. These differently colored portions of the liquid wereseparately withdrawn and analyzed. The results are tabulated in thetable immediately below:

Percent Refractive Percent Stream Fatty Index Carotene Acids This typeof operation is indicative of the extent of the separation that ispossible with the equipment and under the conditions described. It is tobe noted that most of the carotene can be separated by the process. 7

Example 2 Percent Percent Stream Carotene Fatty Acids Volume The topproducts obtained in Examples 1 and 2 were allowed to stand forapproximately one month while being exposedto air. It was observed thatthe products turned from a light orange to a yellow color.

This change is believed to result from oxidation and to indicate thatthe natural anti-oxidants, i. e., the tocopherols, had concentrated inthe lower fraction enriched in carotene.

Example 3 A number of separations were carried out in a verticalaluminum plate column having an effective height of six feet and abreadth of 19 inches. The crude palm oil was preheated to F., introducedinto the column midway between the ends of the slit, and the hot andcold fractions were withdrawn from the top and bottom of the column,respectively. The temperatures of the hot and cold walls and the slitwidth of the column, the rate of tene in the bottom fractions and thefeed are listed in the table below:

Percent Carotene Ratio of Temperature Concentration Carotene Ratio ofSlit Feed Cone. in with Width, Rate, Bottom drawal Remarks Inches inBot- Fraction Hot Cold in Feed tom and Rates W311 W311 Fraction Feed 303126 030 480 0893 0938 1 50/50 CF-CIIB. 293 134 .029 660 .0413 .329 8 0/1 GF-CIB. 297 130 029 440 113 201 1. 74 10/1 EF. 289 126 029 440 0968254 2. 62 10/1 EFdried. 297 133 029 660 0733 217 2. 96 10/1 EF-drled.294 136 044 194 057 0936 1 64 7. 4/1 EF-drled. 283 155 019 218 0761042 1. 37 9. 5/1 EF-dried. 293 126 030 214 0542 133 2. 46 10/1EF-dried. 293 127 030 228 077 175 3. 02 9. 6/1 CF-drled. 292 126 030 4400513 183 3. 57 10/1 OF-dried. 293 133 030 224 0914 190 2. 08 10. 7/1CF-RBE. 294 135 030 414 0932 404 4. 34 9.7/1 OF-RBE.

feed and carotene concentration of the crude palm oil fed to the column,the ratio of withdrawal rates at the top and bottom of the column, andthe concentration of carotene in the bottom fraction are listed in thetable immediaely below:

. Carotene Cold Feed Carotene Ratio E 9 Wan Wall gg Rate, Gone. in ofWithfigg S Temp., m1./ Feed, drawal Fraction F. hour Percent RatesPercent The temperatures of the hot and cold walls were measured bythermocouples at various locations in each of the opposed aluminumplates. The reason for the spread in cold wall temperatures is believeddue to ineflicient circulation of the cooling water.

The higher concentrations of carotene in the fraction withdrawn at thebottom of the column are believed to be surprising in view of theinitial low concentrations thereof in the crude palm oil subjected tothermal diffusion. Since the degree of separation obtainable by thermaldiffusion is a function of the temperature gradient, it is evident thatseparations of even superior quality are possible with more uniform andadequate cooling of the cold wall to a temperature of the order of aboutto F.

Example 4 A number of separations were carried out in the verticalaluminum plate column described in Example 3. In some of theseparations, as noted in the last column of the table, a miscible thirdcomponent such as 15% by volume chlorobenzene (ClB) or 0.5% by Weightrice bran extract (RBE) was added to the feed and in some of theseseparations and others, the palm oil was dehydrated before beingintroduced into the thermal diffusion column. Crude palm oil waspreheated to 110 F., introduced into the column at the top adjacent thecold wall of the slit or at the center (as indicated by EF and CF,"respectively, under Remarks), a carotene-enriched fraction was withdrawnfrom adjacent the cold wall or at the bottom of the column and acarotene-impoverished fraction was withdrawn from adjacent the hot wallor the top of the column. The average hot and cold wall temperatures,the slit width, the rate of feed of crude palm oil, the concentrationsof carotene in the feed and in the bottom fraction, the ratios of ratesof withdrawal of the top and bottom fractions, and the ratios ofconcentration of caro- The results show that higher efficiencies ofseparation are obtained with higher feed rates and lower ratios ofproduct withdrawal, and that at a suitably high feed rate and low ratioof product withdrawal it is possible to obtain a carotene-enrichedfraction that is valuable for further processing to produce concentratedcarotene as well as a carotene-impoverished fraction useful as abyproduct because of its lighter color. The data in the table furtherindicate that even superior results are obtainable by (a) dehydratingthe palm oil before subjecting it to thermal diffusion, ([1) adding tothe feed a material, such as chlorobenzene, that has a lower specificheat and viscosity and a higher density than palm oil, and (0) adding tothe feed an anti-oxidant such as rice bran extract.

It is apparent that modifications and changes in the method describedwill occur readily to those skilled in the art upon reading thisdescription. All such modifications and changes are intended to comewithin the scope of the appended claims.

We claim:

1. Method of concentrating carotene in palm oil which comprises forminga thin film of palm oil confined by opposed surfaces of heat-conductiveinert material, said surfaces being closely and substantially uniformlyspaced apart between 0.01 and 0.15 inch, heating one of said opposedsurfaces to a higher temperature than the temperature of the othersurface to maintain a temperature gradient across the film of oil, thetemperature of the hotter surface being not over about 300 F. and thetemperature of the cooler surface being not under about 105 F.,withdrawing from the film a carotene and tocopherol-emiched fractionconcentrated by thermal diffusion adjacent the cooler surface, andwithdrawing from the film a lighter-colored, carotene andtocopherol-improverished, fatty acid-enriched fraction concentrated bythermal difiusion adjacent the hotter surface.

2. Method defined in claim 1 wherein the ratio of the rate of withdrawalof the carotene-enriched fraction to the rate of withdrawal of thecarotene-impoverished fraction is below about 1 to 10.

3. Method defined in claim 1 wherein the palm oil is dehydrated beforebeing subjected to thermal diffusion.

4. Method defined in claim 1 wherein an inert, viscosityreducing agentis added to the palm oil before the palm oil is subjected to thermaldifiusion.

References Cited in the file of this patent UNITED STATES PATENTS2,313,747 Buxton May 11, 1943 2,482,635 Petering et al. Sept. 20, 19492,541,069 Jones et al. Feb. 13, 1951 2,562,970 Thompson Aug. 7, 19512,615,927 Passino et al. Oct. 28, 1952

1. METHOD OF CONCENTRATING CAROTENE IN PALM OIL WHICH COMPRISES FORMINGA THIN FILM OF PALM OIL CONFINED BY OPPOSED SURFACES OF HEAT-CONDUCTIVEINERT MATERIAL, SAID SURFACES BEING CLOSELY AND SUBSTANTIALLY UNIFORMLYSPACED APART BETWEEN 0.01 AND 0.15 INCH, HEATING ONE OF SAID OPPOSEDSURFACES TO A HIGHER TEMPERATURE THAN THE TEMPERATURE OF THE OTHERSURFACE TO MAINTAIN A TEMPERATURE GRADIENT ACROSS THE FILM OF OIL, THETEMPERATURE OF THE HOTTER SURFACE BEING NOT OVER ABOUT 300* F. AND THETEMPERATURE OF THE COOLER SURFACE BEING NOT UNDER ABOUT 105* F.,WITHDRAWING FROM THE FILM A CAROTENE AND TOCOPHEROL-ENRICHED FRACTIONCONCENTRATED BY THERMAL DIFFUSION ADJACENT THE COOLER SURFACE, ANDWITHDRAWING FROM THE FILM A LIGHTER-COLORED, CAROTENE ANDTOCOPHEROL-IMPROVERISHED, FATTY ACID-ENRICHED FRACTION CONCENTRACTED BYTHERMAL DIFFUSION ADJACENT THE HOTTER SURFACE.